The Lake Pátzcuaro salamander exhibits some highly unusual and distinct features, indicative of its evolutionary distinctiveness, including its rare “neotenous” life history, whereby the species never develops into an adult but instead retains its juvenile characteristics throughout life, essentially achieving reproductive maturity whilst still in its undeveloped larval form. The salamanders are harvested both for human consumption and for medicinal purposes as they are thought to be effective in addressing respiratory problems. Known only from Lake Pátzcuaro (or Lago de Pátzcuaro) in north-western Michoacan, Mexico, it is crucial that this habitat is conserved to secure the future survival of the species.

Urgent Conservation Actions

Conservation of remaining suitable habitat is an urgent priority in order to prevent the species’ extinction in the wild.

There have been claims that a subspecies of the Lake Pátzcuaro salamander is found further inland to the north-east in San Juan del Río, Querétaro, but this is doubtful due to the animal’s entirely aquatic nature which would make it unlikely that the species could disperse between unconnected water bodies.

Recently, Lake Pátzcuaro salamanders have been used in research as a counterpoint to the more common captive-bred axolotl (another species of mole salamander and an EDGE amphibian: Ambystoma mexicanum). Lake Pátzcuaro salamanders have been hybridised in the laboratory with axolotls, which means they have been bred together to combine their characteristics. These hybridised salamanders have been used in comparison studies involving their mitochondria (the energy generating bodies within cells).

The family Ambystomatidae is also referred to as the mole salamanders because many live in burrows for much for their lives. They are found only in North America (from Canada down to Mexico), the majority (unlike the Lake Pátzcuaro salamander) metamorphose from aquatic larvae to become terrestrial adults that are rarely seen except in breeding season, when they migrate to ponds to mate and deposit eggs.

The scientific name for the Lake Pátzcuaro salamander, Ambystoma dumerilii, is after Augusto Dumeril, Professor of Herpetology and Ichthyology at the Natural History Museum of Paris at the time of this species’ decription in 1870.

Evolutionary Distinctiveness

Order: Caudata

Family: Ambystomatidae

The family Ambystomatidae or “the mole salamanders” is included within the four earliest or most primitive family lineages of the order “Caudata” (the salamanders), diverging from all other salamanders in the Early Cretaceous period over 140 million years ago, around five million years before the koala and dolphin lineages diverged from their common ancestor. The small number of species that represent the genus Ambystoma are highly evolutionarily distinct members of both the salamanders and the amphibians as a whole.

The Lake Pátzcuaro salamander exhibits some highly unusual and distinct features, indicative of its evolutionary distinctiveness, including its rare “neotenous” life history, whereby the species never develops into an adult but instead retains its juvenile characteristics throughout life, essentially achieving reproductive maturity whilst still in its undeveloped larval form. There are a couple of theories for why neoteny (also referred to as paedomorphosis) develops in some mole salamanders. One idea is that the production or effectiveness of the hormone thyroxine is compromised, either by the species living in water bodies containing insufficient iodine (which is required in the manufacture of thyroxine by the body) or in water temperatures that are too cold for the thyroxine to be effective. This impacts upon the development of the species and sexually mature adults never develop adult characteristics but remain in the larval form. A second theory suggests that species evolving in pools surrounded by hostile terrestrial environments develop aquatic lives to obviate the need to exit the relative safety of their watery home. This is a common trait in species that inhabit high-elevation ponds.

Description

The Lake Pátzcuaro salamander is an Ambystomatid or mole salamander known only from Lake Pátzcuaro in north-western Michoacan, Mexico, at an elevation of 1,920 meters above sea level. Mole salamanders are medium to large, stocky salamanders, usually measuring between 90 to 350mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. Males are often larger than females, owing to their longer tails. Ambystomatids generally exhibit both aquatic “neotenic” larval (or aquatic and permanently juvenile in form with external, feathery gills) and terrestrial “metamorphosed” (or ground-dwelling, fully developed adult in form with reduced gills) stages in their wild populations. Ambystomatids are often boldly patterned as adults, with well-developed “costal” grooves (successive vertical grooves along the sides of the body), especially the metamorphosing varieties. They have a rather flattened body with a wide, flattened head, a large mouth and smooth skin with many glands. The tail is roundish or laterally compressed, and, during the breeding season, males have a very swollen cloacal zone (the region around the reproductory and excretory opening in amphibians located underneath the base of the tail).

The Lake Pátzcuaro salamander is a neotenic variety of Ambystomatid which results in adults that have long, heavily filamented external gills, gill slits lined with tooth-like gill rakers, and caudal fins along the tail to facilitate swimming. The species is moderately sized, reaching lengths of about 260 mm, with the tail accounting for nearly 50% of this measurement. Lake Patzcuaro salamanders were originally described as possessing a reddish-purple skin colouration along their dorsal (or upper) surface, with a white underbelly. They have also been described as being yellowish in colour. The species is recognised by its large head and reduced limbs. The skin of the head and back is evenly covered in gland pits which secrete a milky liquid which has an unpleasant odour and a bitter taste.

Ecology

The species does not metamorphose, which means it remains outwardly in its juvenile or larval aquatic physical form. As its larval characters are retained throughout its adult life it is known as a “neotenic” salamander because it achieves sexual maturity without developing adult characteristics. This would be akin to a tadpole being able to breed without ever turning into a frog. The Lake Pátzcuaro salamander therefore never becomes terrestrial and lives permanently in water. Once the eggs are laid in water they are left to develop with no further participation by either parent. This species does not exhibit parental care. The Lake Pátzcuaro salamander is known to have a winter breeding season and feeds by suction, eating many types of invertebrates. No field studies to investigate further aspects of the species’ ecology have been conducted.

The foul-smelling, bitter tasting milky liquid that is secreted through glands in the skin of this species functions as a defense mechanism again predators.

Habitat

The habitat of the Lake Pátzcuaro salamander is only found in Lake Pátzcuaro (or Lago de Pátzcuaro) where this species remains fully aquatic throughout its life. Lake Pátzcuaro is a high altitude lake in the Mexican state of Michoacán, located in the Mesa Central region of the country, which is home to many isolated salamander species in the genus Ambystoma.

Distribution

Known only from Lake Pátzcuaro (or Lago de Pátzcuaro) in north-western Michoacan, Mexico, at 1,920m above sea level.

No population data is available, but the Lake Pátzcuaro salamander is believed to be in very serious decline, and might be close to extinction. Recent declines in the catch by local fishermen indicates a severe population crash (based on information from 2003).

Population Trend

No population data is currently available, although the population trend is assumed to be in decline in the IUCN Red List of Threatened Species based on recent declines in catches of this species by local fishermen.

Status

Listed as Critically Endangered on the IUCN Red List of Threatened Species because its extent of occurrence is less than 100km sq. and its area of occupancy is less than 10km sq., all individuals are in a single subpopulation, and there is continuing decline in the number of mature individuals and in the extent and quality of its habitat in and around Lake Pátzcuaro.

Appendix II of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), restricting its international trade to protect the species from over-harvesting in the wild.

Threats

The filling and pollution of the only lake that this species inhabits is the predominant threat to the survival of the Lake Pátzcuaro salamander. Lake Pátzcuaro is an important area for local fisheries and predatory fish have been introduced into the lake, which may be a major problem for the Lake Pátzcuaro salamander species, although it has been able to co-exist with such species for a long time. Lake Pátzcuaro salamanders are harvested both for human consumption and for medicinal purposes (they are supposed to be effective in addressing respiratory problems).

Conservation Underway

The Lake Pátzcuaro salamander does not occur in any protected areas, so the conservation of its remaining habitat is an urgent priority in order to prevent its extinction in the wild. However, this species is protected under the category Pr (Special Protection) by the Government of Mexico and received further protection from over-exploitation and harvesting from the wild by being placed on Appendix II of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), which restricts its international trade.

Conservation Proposed

Conservation and restoration of the species’ habitat is an urgent priority in order to save this species from extinction in the future. In addition to conserving wild habitat for this species, the IUCN Technical Guidelines for the Management of Ex situ Populations, part of the IUCN Red List of Threatened Species, recommend that all Critically Endangered species should have an ex situ population managed to guard against the extinction of the species. An ex situ population is ideally a breeding colony of a species maintained outside its natural habitat, giving rise to individuals from that species that are sheltered from problems associated with their situation in the wild. This can be located within the species’ range or in a foreign country that has the facilities to support a captive breeding programme for that species. This species has already been bred in captivity for laboratory studies, and so captive animals could be a source of new individuals to repopulate natural habitats.

However, any ex situ conservation measure is rendered unhelpful if there remains insufficient natural habitat in which to release captive bred populations in the future. Clearly protected areas, sensitive land use techniques, habitat restoration and studies of the effect of introduced predatory fish populations upon this species are of paramount importance to rescuing this Critically Endangered mole salamander from extinction in the wild. Studies are needed to evaluate the sustainability of the current harvest of Lake Pátzcuaro salamanders, as well as the impacts of introduced predatory fish. This latter information is particularly important since the Lake Pátzcuaro salamander is unique among the aquatic mole salamanders in its apparent long-term coexistence with the introduced largemouth bass (Micropterus salmoides) for the last 60 years, indicating that current predatory fish populations may be a lesser threat to this species in the wild. Working with local communities on initiatives concerning habitat conservation and the reduction of fishing of Critically Endangered species like the Lake Pátzcuaro would also be highly beneficial to environmental management in this area.